This invention relates to a compact, easy to assemble, low cost paper shredder.
Generally, there are two types of cutting mechanisms, "straight cut" or "strip" and "cross cut." A straight cut mechanism comprises a pair of parallel cutting cylinders that contain a series of spaced apart circular cutting disks arranged along the axis of the cylinder. The cutting disks on one cylinder are interleaved with the cutting disks on the other cylinder. The individual cutting disks typically are roughed about the periphery or have a large number of small teeth placed about the periphery of the disk.
The problem with these types of cutters is that the paper is shredded into narrow strips typically as long as the sheet of paper which has just been shredded. Thus, it is possible to reassemble the strips so that the original document can be reproduced.
In contrast, a cross cut type mechanism cuts the paper into small chips or very small strips. Thus, it is sometimes preferable to use a cross cut shredder to maximize the destruction of the paper and to minimize the volume of the waste material.
A cross cut cutting mechanism also comprises a pair of parallel cutting cylinders that contain a series of spaced apart cutting disks arranged along the axis of the cylinder. Each of the cutting disks, however, have less teeth placed about the periphery of the disk compared to the number of teeth on the disks of a straight cut type mechanism. For example, U.S. Pat. No. 4,860,963 shows a cross cut type cutting mechanism where each cutting disk has between 12 and 24 teeth. It also shows that the teeth on one cylinder inter-mesh and overlap with the teeth on the other cylinder.
A particular problem with cross cut mechanisms is the strain on the motor when the teeth engage the paper as a result of the resistance of the paper to being cut. Thus, it has been suggested to displace adjacent cutting disks or their teeth from one another to form a large pitch helix to lessen the cyclical strain on the motor. Also, if the tooth tip is shaped in the form of a V-notch, the tips tend to wear easily and can fracture when encountering a foreign object such as a paper clip.
Moreover, the problem with both of these types of cutting mechanisms is that after the paper has been shredded, it tends to accumulate in the cutting mechanism and, if not prevented, eventually cause the mechanism to be jammed. Particularly in the straight cut mechanism, after the paper has been cut into strips, the strips tend to wind around the cutting disks and spacers, clogging the cutting mechanism. In cross cut mechanisms, the shredded chips tend to follow the direction of the cutting cylinders and eventually clog the cutting mechanism.
To solve this problem it has been suggested to provide a stripping means to strip away the cut paper. Typically, the stripping means consist of a serrated member or a comb type member having teeth which protrude in the spaces between the individual cutting disks. These members can be located on the outward or post-shredder side of the cutting mechanism. For example, U.S. Pat. No. 4,068,805 shows a comb means rigidly placed at the exit of the cutting mechanism.
Another method of providing a stripping means in shown in U.S. Pat. No. 3,033,064 which discloses a pair of combs each having a series of spaced teeth that project into the spaces between each cutting disk to remove the cut strips of paper. Each comb is rigidly mounted so that the teeth protrude into the side of the cutter shaft opposite the cutting area of the cutting mechanism. In addition, they are circular shape so that they wrap around the series of cutting disks.
In addition, it has been suggested to provide a comb type member before the cutting mechanism. The comb then guides the uncut paper into the cutting mechanism. U.S. Pat. No. 4,018,392 shows a pair of combers attached to support rods, each comber having a tongue protruding forward of the cutting mechanism to comb and direct the material being fed to the cutting surfaces of the cutting mechanism.
The problem with these shredders and others is that a number of individual parts are required. Separate parts are required for the comb assembly and for mounting to the shredder housing. This increases the time and labor required to assemble the shredder which in turn increases the cost of the shredder. Therefore, the present invention is directed to a paper shredder that has few parts and is easy to assemble. The shredder includes sintered metal cutting disk units having teeth with a raked piercing tooth and a flat tooth. This will result in a paper shredder that has a lower cost than conventional paper shredders.
In addition, the present invention provides a stripper that effectively prevents the shredded chips from a cross cut mechanism from clogging the mechanism.